Some conventional vehicle lighting units to be mounted on a vehicle body have been known to project light through a transparent plate inclined with respect to the front-to-rear direction of the vehicle body. For example, a high-mount stop lamp to be mounted in a rear portion of a vehicle body can project light rearward through a glass car window (rear window) inclined downward toward its rear end with respect to the vehicle body.
On the other hand, vehicle lighting units that can control light emitted from a light source by means of a light-guiding lens disposed in front of the light source have been widely used to illuminate the front face of the light-guiding lens with light. The light-guiding lens of such a vehicle lighting unit can be formed symmetrical with respect to two directions (for example, a vertical direction and a horizontal direction) orthogonal to the optical axis of the light source with the optical axis as a symmetrical axis. As a result of this configuration, the light distribution thereof can be controlled to be symmetrical with respect to the two directions around the optical axis. Examples of this type vehicle lighting unit may include those described in Japanese Patent Application Laid-Open No. 2011-222339 (or US2011/0249462A2 corresponding thereto).
In a vehicle body incorporating this type of vehicle lighting unit, the transparent plate, or the rear car window, positioned in front of the vehicle lighting unit may be provided with a light-shielding member for concealing portions of the lighting unit other than the front face of the light-guiding lens, which are portions unwanted to be seen from outside. Specifically, in a vehicle body incorporating a high-mount stop lamp, portions of a car window above and below the portion thereof just in front of the light-guiding lens of the lamp may be provided with black ceramic light-shielding coating serving as a light-shielding member, as illustrated in FIG. 1.
However, suppose that such light-shielding members are provided to an inclined transparent plate (e.g., glass car window) in front of the lighting unit (e.g., high-mount stop lamp), and control of light distribution symmetrical with respect to the optical axis of the light source is performed by the light-guiding lens of the above-described conventional vehicle lighting unit. In this case, light that is slightly obliquely projected from the light-guiding lens and reaches the transparent plate at a position farther from the light-guiding lens to pass therethrough (in a high-mount stop lamp, the light travelling at lower side as illustrated in FIG. 1) may be partly shielded by the light-shielding member (e.g., black ceramic light-shielding coating), so that the amount of light tends to be reduced by the amount shielded by the light-shielding member. Further, the amount of light on that side may fundamentally tend to be reduced because the length of light path within the transparent plate may be lengthened more than that at the other side due to the incident angle with respect to the transparent plate.
In particular, in a high-mount stop lamp, since the required light intensity in a 5D direction from the lamp (a direction downward by 5 degrees from the horizontal level) is regulated by a certain law, if the light in the 5D direction is shielded by the light-shielding coating, the automobiles with the resulting high-mount stop lamp may not satisfy the regulation.